The expression “saturation value” of a two-channel (stereo) audio signal is used herein to denote the value of a parameter indicative of a spatial attribute of (e.g., balance between) the two audio channels indicated by the signal. For convenience, we denote the two channels of a stereo audio signal herein as “Left” and “Right” channels, although we contemplate that a stereo audio signal may comprise two audio channels that are not rendered as left and right channels. For example, any two channels of a five-channel audio signal (e.g., Left and Left Surround, or Right and Right Surround, or Left Surround and Center) may be referred to herein as a stereo audio signal comprising “Left” and “Right” channels.
Examples of the “saturation value” of a frame of stereo audio data include (but are not limited to) values indicative of one of the following spatial attributes of the frame:
strength of the dominant signal component (i.e., the dominant one of the two audio channels indicated by the frame) relative to the strength of the ambient signal component (i.e., the non-dominant one of the two audio channels). This attribute is sometimes referred to as the “saturation” of the frame;
LR saturation: strength of the Left channel of the frame relative to the strength of the Right channel of the frame (i.e., a value indicative of Left-Right balance in the stereo mix); and
SD saturation: strength of a Front channel (determined by the Left and Right channels) of the frame relative to the strength of a Back channel (also determined by the Left and Right channels) of the frame (i.e., a value indicative of Front-Back balance in the stereo mix). For example, the Front channel may comprise samples each of which is the sum of corresponding samples of the Left and Right channels, and the Back channel may comprise samples each of which is the difference between corresponding samples of the Left and Right channels.
Steganography is the technique of sending hidden messages, e.g., by embedding hidden messages in data. Steganographic methods have been used for embedding messages in audio data and other data.
However, until the present invention it had not been known how to embed data in a stereo audio signal comprising frames of audio data by modulating saturation values of the frames. In accordance with typical embodiments of the invention, data are embedded in a stereo audio signal (comprising frames of audio data) by modulating saturation values of the frames, without introducing significant audible artifacts into the signal, and in a manner robust to wideband gain change and resampling (e.g., sample rate conversion) attacks.